CArray of stdext::hash_map<int,int> not possible ( access violation ) ? [MFC]

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From: Adam on 10 Mar 2010 05:23

Hello,

I have problems using CArray<> with hash_map<>. What's wrong with the
following code ?

class A
{
A() {}
A( const A& ) {}
~A() {}
void operator=( const A& ) {}
stdext::hash_map<int,int> m_member;
};

....

A item;
CArray<A> test;
test.Add( item );
test.Add( item );
test.RemoveAll(); // access violation in hash_map<>
destructor ????????

The same code with std::map<> works ok. What is the problem ?.
Everything tested under VS.2005.

Thanks,
Adam

From: Giovanni Dicanio on 10 Mar 2010 05:50

From: Giovanni Dicanio on 10 Mar 2010 05:58

"Adam" <adam_mich(a)gazeta.pl> ha scritto nel messaggio
news:80954482-e4f9-4b54-b24e-949c9d5df047(a)i25g2000yqm.googlegroups.com...

> I have problems using CArray<> with hash_map<>. What's wrong with the
> following code ?
>
> class A
> {
> A() {}
> A( const A& ) {}
> ~A() {}
> void operator=( const A& ) {}

As already written, I susepct there is a missing "public:" in the above
class listing.

Moreover, the usual patterno for assignment operator is:

A & operator=(const A &)

Moreover, if the member-wise copy is OK, and if each data member is a RAII
class that frees its own stuff, you should rely on C++ compiler default
implementation of copy constructor , assignment operator, constructor and
destructor.

In other words, in your case, this should do OK:

<code>

class A
{
public:
//
// Compiler generated default ctor, copy ctor, operator= and dtor are
OK.
//
stdext::hash_map<int,int> m_member;
};

</code>

Note that STL containers are very well composable together.
If you use std::vector instead of MFC CArray, this code will work fine:

<code>

A item;
std::vector<A> test;
test.push_back(item);
test.push_back(item);
test.clear();

</code>

HTH,
Giovanni

From: Adam on 10 Mar 2010 06:57

Hi,

Of course all members of A should be public. My mistake, sorry ! Of
course compiler can generate default copy constructor itself in that
case Of course I should use STL containers. It is old, legacy code
which uses CArray<>. I've just added one member - stdext::hash_map
and got those Access Violation errors.
It is not my production code, it's just a code snippet to reproduce
actual behaviour. Now I have even simpler one :

typedef stdext::hash_map<int,int> MAP;

I found that when I add one element everything is ok :

CArray<MAP> test;
MAP item;
test.Add( item );
test.RemoveAll(); // this is ok !

But when I add two or more elements I get access violation

CArray<MAP> test;
MAP item;
test.Add( item );
test.Add( item );
test.RemoveAll(); // unexpectable access violation !

Do you know what is the reason of those errors ?

Thanks in advance,
Kamil

From: Giovanni Dicanio on 10 Mar 2010 07:31

"Adam" <adam_mich(a)gazeta.pl> ha scritto nel messaggio
news:95879f74-8a60-43af-9483-0bac824a61aa(a)t20g2000yqe.googlegroups.com...

> typedef stdext::hash_map<int,int> MAP;
[...]
> But when I add two or more elements I get access violation
>
> CArray<MAP> test;
> MAP item;
> test.Add( item );
> test.Add( item );
> test.RemoveAll(); // unexpectable access violation !
>
> Do you know what is the reason of those errors ?

These could be error messages generated by the Iterator Debugging feature of
Microsoft VC++'s STL implementation.
In fact, if you disable iterator debugging, these errors disappears (I
verified that with VC9 [VS2008 SP1]:

http://msdn.microsoft.com/en-us/library/aa985939(VS.80).aspx

You can add the following lines in your StdAfx.h, before including STL
headers:

// Disable iterator debugging in debug builds
#if defined(_DEBUG)
#define _HAS_ITERATOR_DEBUGGING 0
#endif

Giovanni

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